Waste heat recovery device of multi-cylinder internal combustion engine

ABSTRACT

A waste heat recovering device for a multi-cylinder internal combustion engine, wherein among a plurality of exhaust pipes extending from cylinders of a multi-cylinder internal combustion engine, a plurality of exhaust pipes unlikely to cause exhaust interference are collected to form one or more collecting pipes. A heat exchanger for recovering heat of exhaust gas is provided in the one or more collecting pipes. Therefore, a waste heat recovering device can be provided, in which the number of heat exchangers is reduced compared to the number of cylinders of the multi-cylinder internal combustion engine to reduce rest periods of the heat exchanger and reduce spaces occupied by the heat exchanger.

This application is the national phase under 35 U.S.C. § 371 of PCTInternational Application No. PCT/JP00/08703 which has an Internationalfiling date of Dec. 8, 2000, which designated the United States ofAmerica.

FIELD OF THE INVENTION

The present invention relates to a waste heat recovering device for amulti-cylinder internal combustion engine.

BACKGROUND ART

Known as waste heat recovering devices of this type are a deviceincluding a heat exchanger in each of a plurality of exhaust pipesextending from cylinders of a multi-cylinder internal combustion engine(see Japanese Patent Application Laid-open No. 56-156407, for example)and a device including a heat exchanger in a collecting pipe which iscollection of a plurality of exhaust pipes extending from cylinders of amulti-cylinder internal combustion engine (see Japanese PatentApplication Laid-open No. 5-340241, for example).

However, the former needs as many heat exchangers as the cylinders, andthus has a problem that, for example, after operation of a heatexchanger in the first cylinder in firing order, further operationthereof cannot be performed until just before an end of an exhaustprocess of the last cylinder in the firing order, causing a long restperiod of each heat exchanger, and each heat exchanger is thus cooledduring the period to reduce heat recovery efficiency. Further, if theformer is for vehicle use, it has problems that an evaporator isprovided in each cylinder to increase a size of an engine itself, forexample, by increasing an interval between adjacent cylinders for theevaporator to be mounted, and that the evaporator occupies a large spacein an engine compartment to result in an impediment to securing spacesfor other components to be located.

On the other hand, the latter has a problem that when a collectingportion is formed at a long distance from an exhaust port in order toavoid exhaust interference, and an evaporator is provided in thecollecting portion, temperature of exhaust gas decreases to reduce heatrecovery efficiency by the evaporator. On the contrary, when thecollecting portion is provided at a short distance from the exhaust portwithout considering the exhaust interference in order to utilizehigh-temperature exhaust gas, the exhaust interference reduces output ofthe internal combustion engine and thus exhaust pulses, thereby reducingthe heat recovery efficiency by the evaporator.

DISCLOSURE OF THE INVENTION

The present invention has an object to provide a waste heat recoveringdevice for a multi-cylinder internal combustion engine in which outputof a multi-cylinder internal combustion engine is rarely reduced, andthe number of heat exchangers is reduced compared to the number ofcylinders of the engine to reduce rest periods of the heat exchanger andreduce spaces occupied by the heat exchanger.

To attain the above described object, the present invention provides awaste heat recovering device for a multi-cylinder internal combustionengine including one or more collecting pipes that are collection of aplurality of exhaust pipes unlikely to cause exhaust interference, amonga plurality of exhaust pipes extending from cylinders of amulti-cylinder internal combustion engine, a heat exchanger forrecovering heat of exhaust gas being provided in the one or morecollecting pipes.

When exhaust pipes extending from a plurality of cylinders whose exhaustperiods partially overlap are collected with their lengths reduced,exhaust interference occurs to reduce output of a multi-cylinderinternal combustion engine. However, even when exhaust pipes extendingfrom a plurality of cylinders whose exhaust periods do not overlap arecollected with their lengths reduced, exhaust interference is unlikelyto occur, thus rarely reducing the output of the multi-cylinder internalcombustion engine.

Configured as described above in this view, the output of themulti-cylinder internal combustion engine is rarely reduced even whenthe exhaust pipes are collected with their lengths reduced. Further, thenumber of the heat exchangers is smaller than the number of thecylinders, thus rest periods of the heat exchangers can be reduced.

Reduction in the length of the exhaust pipe as described above allowsthe exhaust gas to be introduced in the heat exchanger with itstemperature reduction minimized, and also the rest period of the heatexchanger is reduced, thereby allowing increase in heat recoveryefficiency of the exhaust gas. Further, attendant on the reduction ofthe heat exchangers, spaces occupied by them can be reduced to achievereduction in size and cost of the device, which is suitable for vehicleuse.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a waste heat recovering device for aninternal combustion engine;

FIG. 2 schematically illustrates a relationship between an in-linefour-cylinder internal combustion engine and an evaporator;

FIG. 3 illustrates a relationship between a crank angle in the in-linefour-cylinder internal combustion engine and an exhaust period of eachcylinder;

FIG. 4A and FIG. 4B illustrate relationships between operating periodsand rest periods in a plurality of evaporators;

FIG. 5 illustrates a relationship between a crank angle in an in-linethree-cylinder internal combustion engine and an exhaust period of eachcylinder;

FIG. 6 schematically illustrates a relationship between an in-linetwo-cylinder internal combustion engine and an evaporator;

FIG. 7 schematically illustrates a relationship between the in-linethree-cylinder internal combustion engine and an evaporator;

FIG. 8 schematically illustrates a relationship between an in-linefive-cylinder internal combustion engine and an evaporator;

FIG. 9 schematically illustrates a relationship between an in-linesix-cylinder internal combustion engine and an evaporator;

FIG. 10 schematically illustrates a relationship between an in-lineeight-cylinder internal combustion engine and an evaporator;

FIG. 11 schematically illustrates a relationship between a V-typesix-cylinder internal combustion engine and an evaporator;

FIG. 12 schematically illustrates a relationship between a V-typeeight-cylinder internal combustion engine and an evaporator;

FIG. 13 schematically illustrates a relationship between a V-typeten-cylinder internal combustion engine and an evaporator; and

FIG. 14 schematically illustrates a relationship between a V-typetwelve-cylinder internal combustion engine and an evaporator.

BEST MODE FOR CARRYING OUT THE INVENTION

In FIG. 1, a waste heat recovering device 2, to which Rankine cycle isapplied, of a multi-cylinder internal combustion engine 1 comprises anevaporator 3 as a heat exchanger for generating a vapor having a raisedtemperature and a raised pressure, that is, a raisedtemperature/pressure vapor, using waste heat, for example, the exhaustgas of the internal combustion engine 1 as a heat source; an expander 4for producing output by expansion of the raised temperature/pressurevapor; a condenser 5 for liquefying a vapor having a dropped temperatureand a dropped pressure, that is, dropped-temperature/pressure vapordischarged from the expander 4 after the expansion; and a supply pump 6for supplying liquid, for example, water, from the condenser 5 to theevaporator 3.

In FIG. 2, a multi-cylinder internal combustion engine, in this case, anin-line four-cylinder internal combustion engine 1 has first to fourthcylinders I to IV, and their firing order is the first cylinder I, thirdcylinder III, fourth cylinder IV, and second cylinder II as denoted byArabic numerals in parentheses (1) to (4) in FIGS. 2 and 3. In FIG. 3,an angle line a is a diagram of a lift of an exhaust valve, thus aninterval from one edge to the other edge of the angle line a shows aperiod when the exhaust valve is opened, that is, an exhaust period b.Therefore, exhaust periods b of the first and third cylinders I, III;the third and fourth cylinders III, IV; the fourth and second cylindersIV, II; and the second and first cylinders II, I partially overlap, sothat exhaust interference occurs when, for example, exhaust pipesextending from the first and third cylinders I, III are collected withtheir lengths reduced.

In this case, for the first and fourth-cylinders I, IV and the secondand third cylinders II, III, their exhaust periods b do not overlap andhence, the exhaust interference rarely occurs. Thus, as shown in FIG. 2,exhaust pipes 11, 14 extending from the first and fourth cylinders I, IVand exhaust pipes 12, 13 extending from the second and third cylindersII, III unlikely to cause the exhaust interference are shortened, andtwo collecting pipes 7 that are collection of the exhaust pipes 11, 14and 12, 13, respectively are formed and provided with first and secondevaporators 21, 22, respectively.

By the configuration as described above, even when the exhaust pipes 11,14 and 12, 13 are collected with their lengths reduced, the exhaustinterference is unlikely to occur, thus rarely reducing the output ofthe internal combustion engine 1. The number of evaporators is “two”,which is smaller than “four”, the number of cylinders, so that restperiods of the first and second evaporators 21, 22 can be reduced.

FIG. 4A shows operating periods and rest periods of the first and secondevaporators 21, 22 in an embodiment in FIG. 2, and FIG. 4B showsoperating periods and rest periods of the first to fourth evaporators ina conventional example. In the drawings, reference characters I to IVdenote the first to fourth cylinders in an exhaust process. As isclearly shown in FIGS. 4A and 4B, the rest period of each of the firstand second evaporators 21, 22 in the embodiment is one third that of theconventional example since the first and second evaporators 21, 22 arealternately operated.

Reduction in lengths of the exhaust pipes 11 to 14 as described aboveallows the exhaust gas to be introduced in the first and secondevaporators 21, 22 with its temperature reduction minimized, and alsothe rest periods of the first and second evaporators 21, 22 are reduced,thereby allowing significant increase in heat recovery efficiency of theexhaust gas.

Further, attendant on the reduction of the heat exchangers, spacesoccupied by them can be reduced to achieve reduction in size and cost ofthe device, which is suitable for vehicle use.

The above described exhaust interference becomes a problem for in-linefour- or more cylinder internal combustion engines, and in athree-cylinder internal combustion engine, explosion intervals are longat crank angles, so that exhaust periods do not partially overlap amongfirst to three cylinders I to III as shown in FIG. 5, thus exhaustinterference is unlikely to occur. This applies to a two cylinderinternal combustion engine. The present invention is also applied to atwo- or three-cylinder internal combustion engine.

FIGS. 6 to 10 show examples of various kinds of in-line multi-cylinderinternal combustion engines 1 to which the invention is applied. In thedrawings, Roman numerals I to VIII denote first to eighth cylinders,Arabic numerals in parentheses denote firing order of the cylinders,reference numerals 15 to 18 denote exhaust pipes, and reference numerals23 and 24 denote third and fourth evaporators. In an in-linefive-cylinder internal combustion engine 1 in FIG. 8, an exhaust pipe 13of a third-cylinder III is separately provided with a third evaporator23. In an in-line three-or less cylinder internal combustion engines,the exhaust pipes are shortened and collected into one. On the otherhand, in an in-line four-, five- or six-cylinder internal combustionengine, with respect to an nth cylinder in the firing order, a cylinderto be collected is an n+2 or more cylinder in the firing order with oneor more places in the firing order skipped. In an in-line seven-, eight-or nine-cylinder internal combustion engine, with respect to an nthcylinder in firing order, a cylinder to be collected is an n+3 or morecylinder in the firing order with two or more places in the firing orderskipped. In an in-line ten-, eleven- or twelve-cylinder internalcombustion engine, with respect to an nth cylinder in firing order, acylinder to be collected is an n+4 or more cylinder in the firing orderwith three or more places in the firing order skipped.

FIGS. 11 to 14 show examples of various kinds of V-type multi-cylinderinternal combustion engines to which the invention is applied. In thedrawings, reference character L denotes a left column and referencecharacter R denotes a right column, and Roman numerals and Arabicnumerals in parentheses denote the same as described above. In thiscase, assuming that each of the left column L and the right column R isan in-line engine, cylinders to be collected are selected in accordancewith the case of the in-line multi-cylinder internal combustion engine.

From the in-line multi-cylinder internal combustion engines 1 in FIGS. 6to 10 and the V-type multi-cylinder internal combustion engines 1 inFIGS. 11 to 14, it is apparent that the number of evaporators is smallerthan the number of cylinders.

What is claimed is:
 1. A waste heat recovering device for amulti-cylinder internal combustion engine, comprising: n, where n isgreater than 1, exhaust pipes extending respectively from n cylinders ofthe multi-cylinder internal combustion engine; at least one and lessthan n collecting pipes for collecting exhaust from said n exhaustpipes; a heat exchanger for recovering heat of exhaust gas beingprovided in each of said collecting pipes; where each of said collectingpipes are connected to exhaust pipes of cylinders spaced in firing orderso as to reduce exhaust interference and situated at a distance fromcorresponding cylinders which is short enough to normally cause exhaustinterference; where a number of heat exchangers provided is less thanthe number n of the cylinders and a total of periods when each heatexchanger receives a supply of exhaust gas per cycle of the engine islonger than a period of one exhaust stroke of each cylinder.
 2. A wasteheat recovering device for a multi-cylinder internal combustion engineaccording to claim 1, further comprising a Rankine cycle system havingan evaporator for generating a vapor with a raised pressure, usingexhaust gas as a heat source; an expander for producing output byexpansion of the vapor; a condenser for liquefying a vapor, which isexhausted from the expander, with a dropped pressure after saidexpansion; and a supply pump for supplying liquid from the condenser tosaid evaporator, said heat exchanger functioning as said evaporator.